91 Nitrogen/protein measurement by Dumas or Kjeldahl methods for Australian grains.

D. C. Mugford (1), G. P. Fox (2), and A. B. Blakeney (1). (1) BRI Australia Ltd., North Ryde, NSW 2113; (2) QDPI, Toowoomba, QLD 4350, Australia.

The dominance of the Kjeldahl method for total nitrogen measurement has been under threat in recent years by the challenge of safer, cleaner instruments employing the Dumas (combustion) principle. Reported comparisons of the two methods offer various conclusions, although several have indicated that results by Dumas were slightly greater than those by the Kjeldahl method. The Australian Grains Research and Development Corporation recognised the significance of methods for nitrogen measurement in grains by its support for an investigation by the RACI Cereal Chemistry Division. A study of the two methods was made in one laboratory on a broad range of grains, cultivars and nitrogen levels (barley, oat, oilseeds, pulses, sorghum and wheat). Dumas results were found to be significantly greater than Kjeldahl (Copper/Titanium catalyst) and the differences increased with increasing nitrogen levels. This was consistent with 96–99% nitrogen recovery with normal Kjeldahl digestion and there appeared to be some related cultivar × site interactions. A collaborative study of the two methods was then made to assess the differences in the light of between-laboratory variability. Comparative method performance characteristics were also developed for validation of the RACI Cereals Division Dumas method.